This in vitro study compared the marginal adaptation of enamel-bonded mesio-occlusodistal composite resin restorations placed using two different insertion techniques (one-step and two-step) and three different curing techniques (occlusal using opaque matrix and wedge systems and interproximal using transparent matrix systems and either transparent, nonreflecting, or transparent, laterally reflecting wedges). The micromorphology of the enamel-restoration interface and the marginal seal were evaluated after the restorations were exposed to mechanical and thermal stresses. Although the difference was not statistically significant, the marginal quality of the restorations placed with the two-step technique was better than that of the restorations placed with the one-step technique. The restorations cured from the interproxi mal direction had significantly better marginal adaptation than did restorations cured only from the occlusal direction. The quality among the groups of interproximally cured restorations was not significantly different, because all the restorative techniques that were evaluated resulted in generally poor marginal quality.